Reversible Histone Modifications Contribute to the Frozen and Thawed Recovery States of Wood Frog Brains.

Epigenetic regulation, notably histone post-translational modification (PTM), has emerged as a major transcriptional control of gene expression during cellular stress adaptation. In the present study, we use an acid extraction method to isolate total histone protein and investigate dynamic changes in 23 well-characterized histone methylations/acetylations in the brains of wood frogs subject to 24-h freezing and subsequent 8-h thawed recovery conditions. Our results identify four histone PTMs (H2BK5ac, H3K14ac, H3K4me3, H3K9me2) and three histone proteins (H1.0, H2B, H4) that were significantly ( p < 0.05) responsive to freeze-thaw in freeze-tolerant R. sylvatica brains. Two other permissive modifications (H3R8me2a, H3K9ac) also trended downwards following freezing stress. Together, these data are strongly supportive of the proposed global transcriptional states of hypometabolic freeze tolerance and rebounded thawed recovery. Our findings shed light on the intricate interplay between epigenetic regulation, gene transcription and energy metabolism in wood frogs' adaptive response to freezing stress.